A positioning device for a transporting system is known from German Patent Disclosure Document DE-OS 3,445,830, Kuehrer, in which a traveling crane carries two lasers that scan reference elements located on the ground. The reference elements consist of two marking surfaces arranged at a certain distance and a specific direction relative to each other. One of the marking surfaces has a longitudinally extended configuration in the form of a strip and is scanned by one of the laser beams, while the other marking surface has a very small surface dimension and is detected by the second laser beam. Both marking surfaces are arranged in such a way that both can be detected by the respective laser beams only upon reaching a desired position.
This arrangement can control only certain positions established by the marking surfaces within the working range of the transport system. Otherwise, the ground under the crane would be completely covered by the marking surfaces and this space would not be available for depositing loads. In addition, it is possible to control only the travel to end position with the known positioning apparatus.
Coded path indicators with which distances can be absolutely measured are known from "Steuern und Regeln im Maschinenbau" (Control and Adjustment in Machine Construction), 3rd Edition, Europa-Lehrmittel Publishers, Wuppertal. A code reading apparatus is moved along a code carrier and the code marks found on the code carrier are scanned by reading heads. Several code marks form a code word on the code carrier, which represents a direct measurement for the code reading apparatus of the path covered from an established reference point.
In this known apparatus, the code word is formed by code marks on several tracks, which lie side by side along the code carrier. Care must therefore be taken that the tracks lie precisely side by side, and the alignment of the markings is accurate. Also, the reading heads, which are arranged in rows next to each other and crosswise to the direction of motion, must be skewed with respect to reference or clock tracks. If misalignment occurs, for example, by skewing, a skew error arises and code marks from code words lying next to each other are mixed up and read together, thus leading to errors. Such a measurement system is thus limited preferably to applications in which the spatial dimensions are small and a precise guiding of the reading heads with respect to the code carrier can be achieved. In crane construction, large tolerances must be accepted, which makes it impossible to use such a measurement device.
The Invention. It is an object to provide a position indicating apparatus which is highly accurate, without requiring precise alignment of a code reader on a transport carrier with respect to the code carrier located on the rail or track, so that the measurement is effectively insensitive with respect to tilting or tipping of the code reader with respect to the code carrier.
Briefly, code markings are located on the code carrier and placed in a single row, one code marking laterally adjacent, preferably next to another; the code markings are arranged along the code carrier in accordance with a predetermined sequence, and m sequential code markings form a code word. The predetermined sequence is so selected that any sequence of m sequential code markings, and forming a code word, appears only once on the code carrier.
Since only a single code track is present in the system, it is effectively insensitive with respect to tipping or inclination between the code reader and the code carrier. The same code word is always read by the reader independent of inclination angles normally encountered in operation of a conveyor system; this assumes that the inclination is not so extreme that the reading device actually leaves the code carrier, that is, reads beyond the code carrier. Offset in height or level of the code carrier with respect to the reader practically has no effect. This substantially simplifies application of the code carrier to the rail or track so that accurate position of the code carrier on the rail is not required.
The code words occur only once along the carrier. Thus, even after a stop of the transport carrier, for example due to breakdown of the equipment, it is still readily possible to immediately establish the position of the transport carrier or traveling mechanism or trolley or other apparatus, the position of which has to be determined, without moving the respective transport carrier or traveling mechanism. This is of particular importance when high supports are used since, in that case, an error with respect to the true position of the traveling mechanism might, upon restarting, cause considerable damage. Movement for determining the position of the traveling mechanism or transport carrier is to be avoided especially in systems high aboveground, since determining the position by first moving the transport carrier might already cause damage.
Sequences of code marks, which have the above-mentioned property of being placed once along the code carrier can be generated in the simplest way according to the theory of primitive polynomials by means of feedback shift registers. The unique definition of each individual code word is, as numerical theory demonstrates, guaranteed in this way.
In order to be able to determine the position as rapidly as possible and without any movement , the code reading device contains a station with reading heads for each place of the code word, i.e., for a ten-place code word, ten reading stations are arranged next to each other. Their relative distance is equal to the length of a code mark on the code carrier.
In accordance with a feature of the invention, and in order to be able to establish whether the code word supplied by the reading heads is a true code word or has been falsified in that one or several of the reading stations have skipped to the next code mark, while other reading stations read the preceding code mark, without employing additional mechanical means, each station has three reading heads, which are arranged interleaved into each other. In this way, two directly adjacent sets of reading heads serve to generate the code word, while the third set supplies the aid for deciding which of the two sets of reading heads may possibly be associated with an error and which of these reads without error.
Since the code words read off by the code carrier in continuous travel of the trolley are not lexicographically arranged, if the code words are interpreted as a binary number, it is appropriate to convert the code word into a binary number, which corresponds to the number of the code word within the generating code sequence table. The determination of the trolley position is then made after converting the product of the code mark length by the number of the code word read, with respect to the origin of the table, which agrees with the code-carrier origin.
In addition to the above-mentioned purely electronically operating monitoring of the reading heads for possible reading error, electromechanical solutions are also conceivable, in which one of the track rollers supplies a timing signal, which establishes when the information delivered by the reading heads is correct information and when the reading heads lie ambiguously over the edges or limits of a code mark.